Catching a cruise out of Barcelona but flying into Frankfurt. Have 3 days to kill before cruise. Which of these two cities has more to offer for a tourist?
Huh? Why not just fly to Barcelona?
Barcelona, definitely! You will not be disappointed with 3 days in Barcelona.
Previous posters have it right: definitely Barcelona. Frankfurt was doable in an afternoon/evening but Barcelona was barely doable in 3 days.
I would stay in GERMANY for 3 days. Day 1: Ride in trains from Frankfurt airport to Bacharach. Check in to a hotel there. Sleep for a couple of hours, and walk through Bacharach. Day 2: in the morning check out of hotel, ride in train to St. Goar, and ride on a big K-D boat on the Rhine River from St. Goar to Bingen. (You will see several medieval castles on hills, at both sides of the river). Ride in train from Bingen to Mainz, check into hotel (near Mainz train station). Day 3: ride in train from Mainz to Frankfurt airport, fly to Barcelona.
Barcelona is my vote. The city is such "eye candy" with Gaudi's influence prevanlent throughout the city. Plus, you have to launch from Barca anyway, why not just relax before... and not risk missing the boat?